1. Field of the Invention
The present invention generally relates to X-ray image intensifiers and, more particularly to an X-ray microscope utilizing a direct conversion X-ray photocathode in conjunction with an electron multiplier.
2. Description of the Prior Art
X-ray to visible converters are well known in the art but generally use indirect conversion techniques, where an X-ray image is converted to visible light in a scintillator, the visible light (photons) are then converted to a corresponding electron image, and the electrons are multiplied and strike a phosphor display screen to provide an enhanced directly viewable visible image. There are numerous disadvantages in having to convert an X-ray image to a visible light image before generating and multiplying a corresponding electron image. Conversion of an X-ray image to a visible light image is normally accomplished by using a scintillator, as described in U.S. Pat. Nos. 4,104,516, 4,040,900, 4,255,666, and 4,300,046. In each instance, the scintillator exhibits a limited response time, poor spacial resolution and sensitivity, and due to the complicated fabrication techniques and the attendant requirement to use light shielding, the cost is prohibitive.
In panel type X-ray image intensifiers, scintillation noise also becomes a problem, which mostly comes from the exponential pulse height distribution of the micro channel plate (MCP) gain.